The present invention relates to quartz resonators for electronic time pieces.
The shape and electrode construction of a conventional quartz resonator in widespread use today in electronic wristwatches is shown in FIGS. 1A and 1B.
On one resonating arm 1a of a resonator 1 are provided an electrode 2a at the peripheral portion and an electrode 2b at the central portion thereof. On the other resonating arm 1b are provided an electrode 2b at the peripheral portion and an electrode 2b at the central portion thereof. The peripheral electrode of the one resonating arm 1a and the central electrode of the other resonating arm 1b are connected together to form the electrode 2a. In like manner the central electrode of the one resonating arm 1a and the peripheral electrode of the other resonating arm 1b are connected the electrode together to form the other.
As understood from the sectional view in FIG. 1B similar, electrodes are provided on the opposite major surface. Electrodes on the front and rear surfaces of the resonator 1 are connected by the means of connecting electrodes on each major surface. The shape of the resonator and the electrodes are made extremely small by the etching process.
The resonator mentioned above is in popular use and the extremely small-sized quartz resonator has a length L which is less than 6 mm and a width W thereof is less than 1 mm and has the following disadvantages with respect to yield (available percentage) and long-term reliability:
(1) If the resonator is made in an extremely small size so as to enable the small and thin, wristwatch to be made the equivalent resistance R1 of the electrical equivalent circuit of the quartz resonator shown FIG. 2 increases and thereby the current consumption increases and also the dispersion in R1 increases, and as a result the yield thereof falls. PA1 (2) Dispersion in peak temperature To of the frequency-temperature characteristic 3 in FIG. 3 increases and the yield thereof falls. PA1 (3) When the tuning form arms are formed by the etching process, the etching at the fork portion of the turning fork inevitably remains as shown by an oblique line portion 4a in FIG. 4 and a non-linear phenomena and decrease in long-term reliability are brought about by local stress concentration.
A pair of quartz resonators 1 and 1 of the type shown in FIG. 1 are incorporated in an oscillating circuit and connected in parallel (refer in FIG. 16), and the frequency-temperature characteristics, particularly the zero temperature coefficient temperature To (referred to as the peak temperature hereafter) is determined by the cut angle of each of the vibrators 1, whereby flat characteristics such as shown by a curve 26 in FIG. 17 is obtained by coinciding the frequency at the peak temperature to thereby improving the frequency temperature characteristics to serve as a time-standard signal generating source. However the high peak temperature ToH on the high temperature side cannot be sufficiently high. Because when the peak temperature is changed by a change in the cut angle, the maximum peak temperature ToM exists as depicted by a curve 7 in FIG. 5. As a means to change the maximum peak temperature ToM, the thickness of the resonator can be changed. A curve 8 in FIG. 6 shows the relation between ToM and the thickness t. The curve 8 shows the case in which the frequency of the resonator is about 32 KHz, which is the most populary used frequency at present. When a pair of resonators are incorporated, it is necessary to make the resonator small in size, so the resonator taken as an example has; the whole length L: about 4 mm, the whole width W: about 0.6 mm and the spaces between the arms: less than 100.mu.. With respect to the arm space s, since the peak temperature To does not change by a change in the arm spaces s, s.ltoreq.100.mu. was selected in order to make the resonator of small size. The whole length L, the whole width W, the thickness t and the spaces between the arms of the resonator will be discribed later with reference to FIG. 10. As shown by the curve 8, the high peak temperature can be obtained if the thickness t is effectively eliminated, however, if the thickness t is made too small or eliminated, the maximum positional error .delta. becomes large rapidly as shown by a curve 9 in FIG. 7. The positional error .delta. is defined by .delta.=(fA-fB)/fA if the frequency in case of +z-axis in the opposite direction to the gravity is fA as shown in FIG. 8A and in case of +z'-axis in the same direction as the gravity is fB as shown in FIG. 8B. Accordingly, the positional error .delta. of devices which during use assume various positions such as electronic wristwatches should be made small and the thickness t cannot be eliminated. For instance, when a wristwatch exhibiting an error of 10 seconds yearly is realized, the positional error .delta. should be within about 4.times.10.sup.-7 and ToM should be no more than 38.degree. C. In order to realize a wristwatch having an error of 10 seconds yearly ToH.gtoreq.40.degree. C. is necesssary and thereby the condition that the positional error .delta. is within 4.times.10.sup.-7 cannot be satisfied. Accordingly, a resonator having the small positional error .delta. and high peak temperature has been expected.
It is an object of the present invention to improve the characteristics of a quartz resonator for an electronic timepiece, and more particularly to decrease the equivalent resistance and dispersion in the temperature characteristics thereof. It is another object of the present invention to provide an extremely small sized quartz resonator having a positional error within 4.times.10.sup.-7 and a high peak temperature of more than 40.degree. C. when a plurality of quartz resonators are electrically connected in parallel to improve the frequency-temperature characteristics thereof.